Method of treating thorium



36o Drawing.

[TED SITES ATENT OFFICE EDMUND S. DAVENPORT, OF BLOOMFIELD, NEW JERSEY, ASSIGNOB. 'I'O WESTINGHOUSE LP COMPANY, A CORPORATION OF PENNSYLVANIA mnrnon or TREATING momma This invention relatesto the art of metallurgy and more particularly relates .to the art of rendering metals resistant to atmospheric corrosion, and comprises essentially in an electrolytic method of treating the surfaces of highly'reactive and easily oxidizable metals such as thorium, cerium, zirconium, titanium, uranium, etc., whereby the metal body is rendered substantially. resistant to surface corrosion when exposed to atmospheric conditions.

Heretofore many methods have been devised wherein. the processes of atmospheric corrosion or oxidation on exposed metal surfaces have either been arrested or prevented. The surfaces have been coated with various paints, enamels, lacquers, non-corrosive metal s, etc. With some metals one process is applicable and withother metals another process is applicable.

In the manufacture of coherent metal bodies of highly reactive metals, such as thorium, uranium, zirconium, cerium, titanium, etc., the formed and fabricated metal bodies are found to. be highlyreactive towards atmospheric gases, progressively combining with oxygen, nitrogenand hydrogen at the exposed surface to: form amorphous films of oxide, nitride and hydride. .This re action continues indefinitely-"and will cause eventually'entir'e destruction'of the' metal body.

' In some metals, such as aluminum, magnesium, chromium, nickel, etc., the surface oxidation only proceeds to the extent necessary to form-anadherentprotective film thereon which is impenetrable to atmospheric gases. Other metals such as iron form surface oxides which are penetrable to atmospheric gases and corrosion proceeds indefinitelyv.

In the latter class of metals some or these may be so treated chemically as to form on the surface an imparted oxide structure which is of a higher or lower state of chemical oxidation not normal .to the metal, but which is impenetrable to atmospheric gases. Such a Application filed June 4, 1828. Serial No. 282,885.

ways and many other metals may be chemically treated so as to arrest or inhibit surface reaction with atmospheric gases.

The present invention is directed to a method whereby the highly reactive metals mentioned above may be rendered substantially passive or non-reactive towards atmospheric gases.

Another object is to produce the highly reactive metals thorium, uranium, cerium, zirconium, titanium, etc., in a form substantially resistant to atmospheric corrosion.

Other objects and advantages will beapparent as the invention is more fully disclosed.

Broadly considered, my invention contemplates imparting to the surface of these highly reactive metals a closely adherent, gasimpervious film of what I consider to be an oxide compound of the particular metal.

' The means I employ in forming this film is electrolytic, thatis, I make the metal the anode in an electrolytic bath and subject it to such a current density as to cause the-formation upon the surface of what I believe to be an oxide compound of the metal. This film in addition to being impervious to gas penetration at room temperatures is, moreover, sufiiciently transparent so that the clean metallic surface underneath is fully visible.

The electrolytic bath'I prefer to employ is comprised mainly of glacial acetic acid containing as an ionizable constituent concentrated nitric acid, in varyingproportions depending upon the metal being treated, current density used, etc.

Other solutions and combinations of electrolytic baths may beemployed in the practice of my invention which will produce essentially the same result as the one described,

that is the release at the anode of oxygen in such a manner as to form this closely adherent oxidized film upon the surface of the metal body.

The main reason why I prefer to use the acetic acid-nitric acid combination is that this solution may be prepared initially substantially. anhydrous, which appears to be a desirable feature in handling such highly reactive metals as contemplated in this disclosure.

The highly reactive metals mentioned, moreover, will require in some instances'some alteration in the chemical components of the bath as mentioned or in the particular current densities applied to produce the result desired, but as a specific embodiment of the nature of my invention I will describe the process I employ in treating thorium so as. to render it substantially impervious to atmospheric corrosion.

It is a well known fact that a freshly olished or exposed surface of thorium Will become rapidly tarnished and darkened on exposure to the atmosphere for a few hours or days. The tarnishing or darkening proceeds from day to day, and depending upon the particular metal under observation will proceed indefinitely.

Formed articles, such as stamped or rolled sheets, wire rods, etc., which are highly compacted, resist the disintegrating eflect of atmospheric gases longer than unworked articles, such as heat treated or semi-sintered ingots having approximately 70 to 80 er cent the denslty o the worked articles. he rate of penetration also depends upon the kind of atmospheric gases present.

In my process the thorium article to be treated is made the anode in an electrolytic article being bath of the type described, and suflicient D. C. voltage impressed across the terminals to free the current therethrough. A variable resistance should be included within the circuit so that the current (amperes) may be controlled Within the rather wide limits required in treating articles of variable size and surface areas.

The current density which I have found to be most efficient in treating thorium rods is approximately 0.25-0.50 amperes per square inch. This, however, may vary within rather wide limits, depending upon the particular treated i. e., rod, wire, bar, or relatively small piece, such as an X-ray target prior to mounting on a backing or small electrodes utilized in the construction of gas rectifiers.

The time interval is a variable factor depending upon the size and'length of the particular thorium article being treated. I

ave determined that with rods of approximately mils. diameter (.080 inches) and approximately 2 inches immersed length, the approximate minimum time interval at the current density mentioned is 2 to 3 minutes. It shouldbe appreciated that the problem is not so much a question of minimum or maximum time interval employed except in so far as the operation of-the invention on a production basis is concerned.

The rogress of the treatment inay be followe by the development of dark grey or black deposit upon the surface of the msae'ra thorium. This black or dark grey deposit may be rinsed ofi in pure ethyl alcohol or other solvent inert with respect to the thorium or other reactive metal used, after which the deposit may be easil rubbed off exposing beneath a clean, metal ic surface.

When properly treated this surface will remain bright and untarnished for prolonged periods of time, and such articles have been found to be increasingly useful in the arts, especially in radio and X-ray appliances where heretofore it has been diflicult to apply the same, due to the surface oxidation and combination with deleterious impurities. q

I have found it advisable in the practice of my invention to properly space the electrodes in the electrolytic bath or to so insulate the anode from the cathode that the full oxidizing effect at the anode may be employed without being deleteriously effected by the hydrogen liberated at the cathode and in treating drawn or swaged thorium wire by my process I may do so in a continuous manner if desired. In treating rods, bars, or small isolated pieces, such as X-ray tar-' gets, etc., provision should be made to continuously rotate the bar or rod during the treating process so as to distribute the anode oxidizing effect.

By the practice of my invention I am able to producea substantially non-oxidizing, non-tarnishing body of the highly-reactive metal thorium which may be utilized in ,the arts. By the practice of my invention I also am able to so treat the surface of other I metals so that they substantially withstand 1 atmospheric corrosion.

There may be many other methods of obtaining the same result and other solution combinations than the one specifically mentioned may be employed in the electrolytic bath, but all such variations and combinations are anticipated as may fall within the following claims.

What is claimed is:

1. The process of rendering thorium msistent to atmospheric corrosion which comprises anodically treating the metal in an electrolytic bath comprised of glacial acetic acid containing a proportion of an ionizable the anode.

2. The process of rendering thorium reto render the metal resistant to atmospheric corrosion which comprises anodically treating the metal in an electrolytic bath comprised of the latter up to approximately 30 percent b volume of the former.

glacial acetic acid and nitric acid, a component bemg present in amounts 1 1'15 constituent capable of yielding oxygen at 

